This invention relates generally to optical information processing and, in particular, to an optical cross bar technique for performing parallel optical logic and arithmetic operations.
There is a fundamental difference between optical circuits, in which the information carriers are photons, and electronic circuits, where the carriers are electrons. In the former case the carriers do not interact with each other, while in the latter they do. This means that in optical devices there exist interconnect possibilities that do not exist with electronic hardware, in particular, interconnected parallel architectures. The invention described herein uses this type of architecture to perform digital arithmetic and logic operations in a completely parallel, single step process. After the inputs are switched on, the output appears in the time it takes a photon to transit the device. No faster computation time is possible.
The invention described herein relies on a mathematical framework similar to that described in the application of C.D. Capps and R.A. Falk, entitled "Parallel Optical Arithmetic/Logic Unit", Ser. No. 019,767, filed concurrently herewith and incorporated herein by reference. The above mentioned disclosure incorporates parallel optical Fourier transform pattern recognition to determine the spacing between the two lighted sources of a linear set of equidistant, coherent point sources. Using a set of (2n-1) recognition filters and thresholds, this technique provides for the determination of the elements of any n by n logic truth table that can be permuted to be anti-diagonal. In particular, residue addition and multiplication can be performed.
Briefly, the aforementioned capabilities lie in the fact that residue arithmetic does not have a "carry" operation; that is, each "bit" in the representation is independent of the other. Thus, for example, addition in residue arithmetic of corresponding "bits" in two numbers can effectively be carried out by a device that is not connected to other "bits", but parallel to other bits. In residue arithmetic, each "bit" in a representation of a number is the decimal value of the number modulo the prime number corresponding to that position, called the "radix". However, never before has there been an optical computing technique that takes advantage of the properties of residue arithmetic and obviates the need for any lenses or filters.
Two dimensional optical computers have been proposed by Schaefer et al in U.S. Pat. No. 3,996,455. Schaefer et al perform arithmetic operations on a pair of matrices whereby an output plane is used to project a two dimensional image whose pattern is indicative of an output state. However, detection of this two dimensional pattern is critical to the correct operation of the computer. Additionally, Schaefer et al disclose only binary coding of data which will not allow one step, parallel processing of a single arithmetic function in residue arithmetic.